Abstract: Since the slide of expansive soil slope is generally characterised by time-dependent properties such as chronicity and gradualness, triaxial unloading creep tests are carried out on the expansive soil specimens by GDS stress path triaxial apparatus. The test results show that the creep curve of expansive soil only shows transient deformation and attenuation creep with low deviatoric stress. When the deviatoric stress reaches a certain value, the creep curve also exhibits attenuation creep, steady creep and accelerated creep, and the velocity in the accelerated stage is nearly constant, different from common soil. Meanwhile, isochronous stress-strain curve of expansive soil indicats that its creep process has nonlinear characteristics, and the nonlinear degree is related to creep time and stress level. When the creep time is longer and the stress level is higher, the degree of nonlinearity is higher. Based on the nonlinear rheological theory, a new nonlinear four-element creep model is presented, in which the standard linear body is connected in series with a nonlinear clay pot. The proposed model can describe the evolution of the axial strain of expansive soil with time under constant confining pressure and triaxial compression stress. According to triaxial compression creep test results of expansive soil, the parameters of the proposed model are inversed by using curve fitting method．The theoretical curves accord well with the test curves, which indicate that the proposed model can describe the creep property of expansive soil. Furthermore, critical failure stress can be obtained based on the creep model. As the confining stress decreases, the ratio of the critical failure stress to conventional shear failure stress decreases, which indicates that creep likely happens on the expansive soil layer closer to slope surface.

Key words: expansive soil, unloading, creep, nonlinearity, creep model